1. Field of the Invention
The present invention relates to a reel for a magnetic tape. More particularly, it relates to a reel comprising a flanged hub used for a magnetic tape cassette.
2. Discussion of Background
A magnetic tape is generally wound around a hub or a flanged hub in a magnetic tape cassette. In a magnetic tape cassette for video, the magnetic tape has to be more correctly wound and safely protected than a magnetic tape for audio. Accordingly, a flanged hub is usually used for a tape reel. The tape reel for video comprises a hub with a lower flange formed integrally therewith and an upper flange. A center boss is formed at the center of the upper surface of the hub, and a plurality of other bosses are arranged around the center boss in the same circle and at equal distances. A plurality of through holes are formed in the upper flange at positions corresponding to the center boss and other bosses. When the tape reel is assembled, the center boss and other bosses are inserted respectively in the center through hole and other holes, and the top of each of the bosses is melted by heat to thereby enlarge the tops, whereby the upper flange is firmly connected to the hub. In the conventional technique of connection using a method of caulking, it is difficult to correctly place each of the bosses on a jig for melting. If caulking operations are incomplete, a sufficient difference of height at the top portion of the center boss and other bosses can not be obtained. Since the tape reel is vertically movable in a range of clearance in the cassette casing, the tape reel may be lifted in operations and a leaf spring provided in the casing, which is used to press only the center boss, is elongated to thereby come in contact with the top of the other bosses. In this case, when the hub is rotated, powder is produced by the contact of the spring with the bosses; uneven rotation takes place or a phenomenon of drop out may occur; this results in erroneous recording or reproducing. Since the top of the bosses is visible through a transparent window formed in the upper half casing, insufficiently caulked bosses reduce the quality of the tape cassette.
The inventors of this application have proposed in Japanese Utility Model Application No. 154283/1987 a magnetic tape cassette having a construction as shown in FIGS. 6a and 6b wherein a hub 14 having a lower flange 10 formed in one-piece with the hub 14 and having a center boss 12 at the center of its upper surface is attached with an upper flange 20 having a center opening 16 to receive the center boss 12 and a plurality of fitting openings 18 formed around the center opening, and a fitting ring 24 made of the same material as the hub 14 and having a center opening 22 to receive the center boss 12 is mounted at the upper part of the hub 14 so as to interpose the upper flange 20 between the fitting ring 24 and the hub 14, followed by connecting the fitting ring 24 by means of the plurality of fitting openings 18 formed in the upper flange 20 by melt-bonding.
However, in the tape reel as proposed, a sufficient strength of connection can not be obtained in a stable manner because the lower surface of the fitting ring 24 is connected to the upper surface of the hub 14 by melt-bonding. In such tape reel, since a gap 26 is formed between the inner circumference of the center opening 22 and the outer periphery of the center boss 12, and a gap 28 is formed between the outer circumference of the fitting ring and the upper flange 20, there results eccentricity in position between the center boss 12 and the fitting ring 24 due to deviations at or during the melt-bonding operations. The eccentricity in position may cause disconnection of the fitting ring 24 from the hub 14 when the magnetic tape cassette is operated. The gap 26 serves to permit insertion of the center boss 12 in the center opening 22 of the fitting ring 24. The gap 28 serves to prevent any crack by a pressing force of the fitting ring 24 to the upper flange 20 when the fitting ring 24 is attached to the hub 14. The eccentric arrangement reduces the quality of the magnetic tape cassette because the tape reel is visible through a display window formed in the cassette.